Impoverished African migrants crowd the night shore of Djibouti city, trying to capture inexpensive cell signals from neighboring Somalia—a tenuous link to relatives abroad. For more than 60,000 years our species has been relying on such intimate social connections to spread across the Earth.

Villagers pray for rain in the Afar desert. A megadrought lasting thousands of years may have bottled up early humans in Africa, making travel risky. A climate shift bringing wet periods likely helped propel the first migration.

Wherever there’s water, camels and their herders appear. Space for the traditional seminomadic life is shrinking though. A wall diverts the Awash River in Ethiopia as part of a project to turn desert into vast sugarcane fields.

Inches beneath the barren surface of Ethiopia’s Afar depression, paleontologists with the Middle Awash Project find tools and other evidence of humans from 60,000 years ago and earlier. An Afar youth holding a traditional knife, or jile, observes the researchers at work in one of the Earth’s hottest places.

Camels travel an unfamiliar way in a truck bound for Djibouti city, where they will be shipped to the Middle East. Camels raised in the Horn of Africa are a valuable export item. Some are bought for racing, others for their milk, but most are auctioned off and slaughtered for their meat, a staple in the gulf states.

A desperate journey ended in a lava field in Djibouti. Dozens of graves and corpses appeared along the route, tragic examples of the Africans who have died crossing this brutal desert on their way to find work in the Middle East.

Wrapped in white to symbolize purity, women arrive for prayer at an Ethiopian Orthodox church in Asaita. An increasing number of Christians from Ethiopia’s highlands come here to work on farm plantations.

An acacia rustles with plastic trash dropped by travelers. Afar nomads use the term Hahai, or People of the Wind, to describe the refugees, deserters, migrant workers, and others who blow through the desert.

An urban oasis, the central market in Djibouti city pulses with traffic. Buses bring migrants who, Salopek says, have changed in a generation from premodern pastoralists to hustling wage-earners in this city of 500,000.

Two dozen men, mainly Ethiopians, languish in a shack in Djibouti city. Most are waiting for relatives to wire money to a smuggler for passage to Yemen. Some 100,000 migrants a year leave the Horn of Africa to look for work.

Backed by old AK-47s, coast guard personnel in Djibouti city monitor the Bab el Mandeb waterway. Early humans left Africa by crossing the strait. Salopek caught a boat here to Saudi Arabia to follow in their path.